1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for minimizing the effective wafer resistance of an electronic lapping guide.
2. Description of the Related Art
Disc drives are well known in the art and comprise several discs, each disc having several concentric data tracks for storing data. A magnetic read/write transducing head carried by a slider is used to read from or write to a data track on a disc. Such sliders, as well as the transducing heads, are typically produced by using thin film deposition techniques. In a typical process, an array of sliders are formed on a common substrate, such as a wafer. The wafer is typically inspected, and is then sliced to produce rows, with a row of sliders in a side-by-side pattern on each row. The rows are then lapped at the surface that will eventually face the recording medium to obtain the desired magnetoresistive (MR) element height (also referred to as the specified stripe height). After lapping, an air bearing pattern is formed on the rows and the rows are diced to produce individual sliders.
With the move to higher areal densities on discs, there is pressure to reduce the stripe height on the sliders. Reducing the stripe height permits an increase in areal densities and signal quality. However, problems emerge as stripe heights decrease. As stripe heights are reduced, seemingly minor variances in the stripe heights from slider to slider will produce different signal amplitudes in each of the sliders. These differing amplitudes make it difficult to control the signal from slider to slider. Thus, though it is desired to reduce the stripe heights, it is also desired that the MR elements for each slider on the row be lapped to the same stripe height.
To achieve reduced stripe heights on the sliders, accurate control of the manufacturing process has become critical. Current designs for controlling the lapping process involve placing one or more electronic lapping guides (ELG) on the row. During the lapping process, material is removed from the surface of the row. As material is removed from the surface of the row, material is likewise removed from the ELGs attached to the row.
The ELG is connected to a lapping controller which provides a current to the ELG and determines the stripe height of the ELG based on resistance between the bonding pad and the grounding pad. The ELGs have a known resistance as a function of height so that as the surface of the row is lapped, the resistance of the lapping sensor changes. The ELGs are monitored during lapping to provide feedback to a control system indicating the amount of material being removed from the row by the lapping device.
The ELG is connected to a lapping controller by either a 2 wire (double pad) connection or a 1 wire (single pad) connection. Though a single pad connection ELG allows for fewer connections to the wafer and more space conservation, precision decreases compared to lapping of a double pad connection ELG. When lapping multiple sliders of a row using single pad lapping, the resistance detected at one ELG may not properly correlate to the resistance detected at the next ELG. This change in resistance can adversely affect proper lapping from one slider to the next.
Thus there is a need for better control of resistance and the effects of that resistance as detected at the ELG during single pad connection lapping of a slider.